1. Field of the Invention
The present invention relates to the photodecomposition of all perfluoroalkyl iodides of general formula C.sub.n F.sub.2n+1 I (where n is a positive integer from 1 to 13) on diamond surfaces as an improved method of fluorination of a diamond surface. This invention also relates to using C.sub.n F.sub.2n+1 I molecules as photochemically activated fluorinating agents, photodecomposing the fluoroalkyl iodide molecule, attachment of the photofragments to the diamond surface and thermal decomposition of the fluoroalkyl ligands. The fluorinated layer produced by this new method has been found to exhibit high thermal stability, comparable to surface layers produced by direct fluorination of diamond with F atoms. A fluorinated diamond surface is made by the disclosed method.
2. Description of the Prior Art
The surface properties of many materials may be significantly improved by the use of diamond film coatings. Diamond films exhibit physical properties making possible the fabrication of long-lived cutting tools, biological implants, optical disks, lenses and windows. [P. K. Bachmann et at., Chemical Engineering News, 67 (20), 24 (1989); J. E. Field, "The Properties of Diamonds", Academic, New York (1979); J. E. Field, "The Properties of Natural and Synthetic Diamonds", Academic, New York (1992); R. Pool, Science, 249, 27 (1990); B. J. Feder, The New York Times, Feb. 21, 1990, p. C4; D. E. Koshland, Jr., Science, 250, 1637 (1990).] In each of these applications, it is desirable to modify the properties of the outer surface of the diamond film itself in order to build in special surface properties of the protective diamond coating.
The chemical modification of diamond surfaces provides one route for producing useful surface properties. One modifier which offers promise for the improvement of the behavior of diamond surfaces is fluorine. [S. K. Ritter, Chemical and Engineering News, 73 (9), 39 (1995).] It has been shown that the strong surface C--F bonds [Handbook of Chemistry and Physics, CRC Press, Boca Raton, Fla. (1982-83), 63 Edition, p. F-199] on diamond provide enhanced lubricity [D. S. Y. Hsu et al., Fourth SDIO/IST ONR Diamond Technology Initiative Symposium, July 1989] and enhanced stability under oxidizing conditions at elevated temperatures [D. E. Patterson et al., Mat. Res. Soc. Symp. Proc., 140, 351 (1989)].
Until now, the fluorination of diamond surfaces has been accomplished only with extreme surface treatment methods involving molecular F.sub.2, atomic F [A. Freedman et al., Appl. Phys. Lett., 57, 1194 (1990); Mat. Res. Soc. Symp. Proc., 204, 571 (1991); Proc. Electrochem. Soc., 91, 494 (1991); New Diamond Sci. Technol., Proc. Internat. Conf., 2, 321 (1991)], XeF.sub.2 [J. F. Morar et al., Phys. Rev. B., 33, 1340 (1986); J. F. Morar et al., Phys. Rev. B., 33, 1346 (1986)], and fluorine-containing plasmas [P. Cadman et al., J. Chem. Soc. Chem. Comm., 654 (1975)]. Each of these surface modification methods involves handling corrosive gases under harsh treatment conditions. In addition, only partial fluorination of the diamond surfaces studied has been achieved using these extreme methods. To the best of the Applicants' knowledge, no one to date has reported the attachment of long chain fluoroalkyl species to diamond surfaces.
In spite of previous methods involving elemental F.sub.2, atomic F, plasmas containing fluorine species and XeF.sub.2, materials which are hard to handle and need special techniques, there still remains a need for an improved method which provides an improved chemical reaction route for producing a fluorinated diamond surface which is stable to high temperatures.